Pulse generating circuit



Sept. 15, 1959 V M, P, FOLEY 2,904,755

' PULSE GENERATING CIRCUIT Filed Oct. 14, 1957 A 29 I R i l2 i o I I :7 l9 l8 E W HI 5 l 1 I h 2| I II I L. ..-J L Fuel Qf. r 22 TIME TIME 0 EELJ EE J ':L

24 EAL/25 in; 1' i 1 D Hi 1/ E TIME 9 as I E? VISA? I H b u 28 9 u o I TIME I INVENTOR. MICHAEL P. FOLEY I BY (112% a I ATTORNEYS United States Pate flice PULSE GENERATING ClRCUlT Michael P. Foley, North Hollywood, Calif.

Application October 14, E57, Serial No. 689,881

2 Claims. (Cl. 331-112) This invention generally relates to pulse generating circuits and more particularly to an improved circuit for flashing a light useful as a roadway barricade warning device.

Many flasher circuits have been proposed heretofore for providing an economical warning device for road or other construction barricades as a substitute for the conventional flame lantern. Most present day electrical circuits for accomplishing the above include a mechanical portion adapted to open or close contacts mechanically and thus effect the desired flashing. Usually, the mechanical portion includes a rocker arm or pendulum-like element electromagnetically actuated for continuous oscillation at a predetermined fixed frequency. An advantage of the present day electro-mechanical arrangements is that they are relatively inexpensive to manufacture and they provide the necessary voltage and discharge current for lighting a gas filled tube such as a Neon bulb. A primary disadvantage is in the maintenance problem inasmuch as the mechanical portions will eventually wear due to mechanical movement. Further, the flasher units employing electro-mechanical circuits are position sensitive and will best operate only when in an upright position.

In an effort to avoid mechanically moving parts in flasher units, some purely electronic systems have been proposed which employ no mechanical movement whatsoever. However, these systems do not provide the required high voltage necessary to discharge a Neon tube or similar gas filled tube. They have been successful with respect to ordinary incandescent lights. However, incandescent type light bulbs require a short period to heat the filament before light is emitted. Further, the intensity of the white light emitted from conventional incandescent bulbs is not as penetrating as that producedby a Neon bulb, for example. Further, the requirement of preheating the filament prior to the emission of light results in a drain on the battery powering the system with the consequent disadvantage that the overall life of the unit, relatively speaking, is short.

Bearing the above in mind, it is a primary object of the present invention to provide a greatly improved flashing unit capable of periodically flashing a Neon type bulb or other gas filled discharged tube at a desired rate and which employs no moving parts and is insensitive to the particular position in which it may be placed.

More particularly, it is an object to provide a flasher unit of the above type to serve as a highway hazard warning which is substantially maintenance-free and is designed to be moisture, dirt, and dust proof.

Still another object is to provide a flasher unit in which the flash rate is adjustable.

Another object is to provide a flasher unit of the above type in which the apparent intensity or flash duration may be controlled independently of the flash rate.

These and many other objects and advantages of the present invention are attained by providing a circuit employin a current source in the form of a battery across minal of the current source and a feedback coil coupled. to the transformer is provided between the base terminal,

of the transistor and the junction point of the resistance and condenser. A secondary winding is provided on the.

output transformer across which is connected a gas filled.

tube such as a Neon tube. The entire circuit with the exception of the Neon tube, battery, on-off switch and,

terminal leads extending thereto is immersed in an epoxy-- resin such that it is rendered substantially shockproof and no possibility of dirt or moisture or the like can enterv the circuit. The whole unit is completely silent in operation.

By making the resistance associated with the condenser variable, the frequency or rate of flashing of the Neon bulb may be controlled within certain limits. Further,

by incorporating a time delay network between the col lector and base terminals of the transistor, and by properly varying the amplitude of the time delay current, the.

duration of the flash of the Neon bulb may be effectively controlled and thus provide an apparent intensity control.

A better understanding of the invention will be had by referring to a preferred embodiment thereof as illustrated in the accompanyin drawings, in which:

Figure l is a schematic circuit diagram of the flasher unit of this invention; and,

Figure 2 illustrates a series of time graphs indicating various wave forms in portions of the circuit useful in explaining the operation of the circuit of Figure 1.

Referring to Figure 1, the circuit comprises a current source in the form of a battery E provided with an olfon switch S and having two power output leads 10 and,

former T having a primary winding 12. One end of the winding 12 connects to the output lead 10 while the other end passes to a collector lead 13 of a transistor 14. The emitter terminal lead 15 of the transistor 14 is in turn connected to the other output lead 11. The secondary winding 16 of the output transformer T in turn is COD: nected across a Neon discharge tube 17.

Also included in the circuit is a feedback coil 18 hav ing one end connected to a junction point 19 between the resistance R and the condenser C and having its other end connected to a lead 20 passing to the base terminal 21 of the transistor 14. Finally, the circuit includesa,

time delay network comprising a variable resistance R and condenser C connected in series.

base terminal lead 21 of the transistor 14.

The feedback coil 18 has a polarity opposite to that' of the primary winding 12 of the transformer T and is positioned in flux coupling relationship with respect thereto.

Referring now to the several graphs in Figure 2, theoperation of the circuit of Figure 1 will be described. Upon closing of the switch S, current from the battery B will pass through the output lead 11 to commence charging of the condenser C. The rate of charge of the E and is plotted as an ordinate against time as, the

abscissa. As shown, the voltage curve increases with Patented Sept. 15, 1959 This network is' connected between the collector terminal lead 13 and time to a point 22. A'tthis time the voltage build up across the condenser C is sufficient to cause the transistor 14 to conduct.

Referringto. the second graph in Figure 2 there is shown the collector current I plotted as a function of time, When the transistor commences conducting", the ccjllec tor current 1,, passes through the primary winding 12building up fluxth'erein until it saturates. During this v ng period, the rate of change of flux in the primary winding 12 induces a reversed polarity current in the feedback coil 18 This feedback current is fed to the base terminal 21 through the lead 20 and augments the flow of current through the transistor whereby a regenk erative effect created and an extremely rapid'rise of' the collector current takes place.

After the primary winding 12 becomes. saturated,.the rate of change of flux therein drops to. zero so that there no longer any induced feedback current in the coil. 18,. As a consequence, the base current fed back is cut off and the transistor ceases conducting. With no more collector current passing through the primary winding 12, the magnetic field collapses which induces a negative dip in the current passing through the primary. This dip is indicated at 24 in the second plot of Figure 2 and infturn serves to induce another current of reversed polarity in the feedback coil 18. This current in the feedback coil 18 is designated I and is plotted in the third graph of Figure 2 with respect to time. Because of: the reversed polarity of the coil 18 with respect to primary winding 12, it Will be noted that the current I} isin the form of a positive pulse.

This positive pulse will momentarily bias the transistor tocut off, but will not hold the transistor cut-off since the voltage across the condenser C cannot change instantaneously. Thus the transistor will again conduct since C still retains substantially the voltage necessary to fife the transistor. This cyclic action in turn causes another piilse to be communicated through the feedback cio 'il 18 andthrough the condenser to the emitter to repeat the process, .giving rise to a series of negative dips indicated in dotted lines at 25 and 26 in the primary winding 12 a .,The various pulses 24, 25, and 26 pass to the secondary Winding 16 by transformer action and result in a series of. discharges of the Neon tube 17 lasting for a dura-, tion designated on the time scale of the second plot of Figure 2 as D. These series of pulses occur in rapid success ion and appear as a steady light of duration D as observed at the Neon tube. When the condenser C loses its charge completely the pulses cease. There is then a short quiescent period and the condenser C will then come mence charging up again providing the switch S is maintained closed.

The cycle is then repeated as indicated in the charge and discharge curves of the first plot of Figure 2. The frequency of the flashes through the discharge Neon light 17 can be readily. controlled by varying the re-v sistance R which varies the period P of charging and discharging of the condenser C. Thus, a frequency control may be readily provided for controlling the number of flashes per second.

An added feature of the circuit of Figure l constitutes the time delay network R'C' connected between the collector terminal 13 and base terminal 21. The effect of this circuit is to give rise to a time shifted feedback 6 designated I and plotted in the third plot of Figure 2 in dotted lines. Since the time delay network is connected directly to the collector terminal, itwill pass a current of similar wave shape to that illustrated as the collector current in the second plot of Figure 2. However, as shown, it will be delayed to the right in time. By making the resistance R variable, the amplitude of this time shifted signal may be varied or attenuated as to both the timing network and the feedback coil 18, the effective base current will constitute the sum of these feedback currents and is plotted in the last plot of Figure 2 as I It will be noted that I includes a prolonged positive portion 28 as a consequence of the time shifted current I This positive portion 28 in the base current holds the transistor 14 cut off such as to prevent repetitions of the negative pulses as indicated by the dotted line pulses 25 and 26 illustrated in the plot for the collector current and allow a sufficient length of time for C to discharge. In other words, the transistor is blocked from passing the subsequent oscillations and the time at which the transistor is blocked may be controlled by the amplitude of the prolonged portion 28. This amplitude is controlled in turn by the attenuating resistance R such that there is efiectively provided a control of the duration D and thus the apparent intensity of the flash as seen in the Neonbulb 17. H

Referring once again to Figure 1, there is illustrated a dash-dot line 29 surrounding all of the circuits illustrated with the exception of the Neon bulb 17, battery E, switch S, and a portion of the leads connected thereto- The circuit contained within the dash-dot line 29 maybe wholly immersed within an epoxy-resin and thus con pletely sealed from moisture, dirt, and dust. The life of the entire circuit Will be limited only by the life of the battery E. The battery E is exterior of the epoxyresin casing 29; it may be simply replaced when' it has become completely discharged. I

From the foregoing description, it will be evident that the present invention provides a greatly improved flasher circuit which is completely electronic in operation with' the attendant advantages of no moving parts and'very high reliability. Further, the output transformer T in: combination with the transistor feedback circuit therefor and timing circuit provides sufficient voltage to fire the:

Neon tube 17 and thus provide the desired Warning flashing signal. such as R and R enable both the frequency and the'dufa tion to be varied independently of each other. v

It is not absolutely essential that the resistance R be included in the circuit, since the inherent leakage resistance in the transistor in the circuit from junction point 19, coil 18, base lead 21, to collector lead 13 and winding 1 2back to lead 10, could serve the same funciton as R except that the feature of being able to vary the frequency could not readily be effected. 7

Other modifications that fall within the scope and spirit of the present invention will readily occur to those skilled in the art. The flashing circuit is, therefore, not to be thought of as limitedto the specific embodiment set forth for illustrative purposes.

What is claimed is: I v I 1. A pulse generating circuit comprising, in combina tion: a current source; a transistor having emitter, col lector, and base terminals; a transformer having primary and secondary windings, said emitter terminal being connected to one side of said current source and said collector terminal being connected to one end of said primary winding, the other end of said primary winding being connected to the other side of said current source; a current feedback coil in flux coupling relationship with said primary winding; a condenser; one end of said feed back coil being. connected to one side of said condenser and the other end of said feedback coil being connected to said base terminal, the other side of said condenser being connected to said one side of said current source; and a time delay networkcomprising an additional condenser and a variable resistance connected in series between said collector terminal and said other end of said feedback coil, whereby the duration of time that said transistor passes current can be varied to control the duration of the pulse of output energy appearing at the indicated by I Since the base terminal lead 21 connects terminals of said secondary winding.

Finally, the provision of variable resistances 2. The subject matter of claim 1, including an additional variable resistance connected between said other side of said current source and the junction of said one end of said feedback coil and said one side of said condenser, whereby said additional variable resistance and said condenser in series together form a fi'equency control circuit connected in parallel with said current source to control the repetition rate of said pulse of output energy.

References Cited in the file of this patent UNITED STATES PATENTS Seaman et a1. June 28, 1938 Browner Nov. 15, 1949 Felker May 8, 1956 Lindsay Dec. 10, 1957 

